The invention relates to a semiconductor device with a semiconductor body provided with a first and a second bipolar transistor in a cascode configuration with collector, base and emitter regions which form pn junctions with one another which extend parallel to a main surface of the semiconductor body, which semiconductor body comprises
a semiconductor substrate of a first conductivity type which forms the collector region of the first transistor and is provided with a connection electrode on a first main surface of the substrate, PA1 a first semiconductor region of the second, opposite conductivity type adjoining the substrate and forming the base region of the first transistor, PA1 a second semiconductor region of the first conductivity type adjoining the first region and forming the emitter region of the first transistor and forming the collector region of the second transistor, PA1 a third semiconductor region of the first conductivity type adjoining the second region and more weakly doped than the second region, PA1 a fourth semiconductor region of the second conductivity type adjoining the third region and a second main surface of the semiconductor body and forming the base region of the second transistor, which fourth semiconductor region is provided with a connection electrode, and PA1 a fifth semiconductor region of the first conductivity type adjoining the fourth region and the second main surface of the semiconductor body and forming the emitter region of the second transistor, which fifth region is provided with a connection electrode.
Two npn or two pnp transistors form a cascode configuration in the semiconductor device, an emitter region of the first transistor at the same time forming a collector region of the second transistor. When the semiconductor device is in operation, the second transistor modulates an emitter current of the first transistor. A cascode circuit has connection electrodes for the collector and base of the first transistor and for the base and emitter of the second transistor.
European Patent no. 0493854 discloses a device of the kind mentioned in the opening paragraph in which the base region of the first transistor is connected to a connection electrode which is present on the second main surface of the semiconductor body. A highly doped connection region is provided between this electrode and the base region of the first transistor in order to connect this electrode to the base region of the first transistor. This connection region surrounds the collector, base, and emitter regions of the second transistor without making contact therewith.
The known device described has the disadvantage that the second transistor is fully driven into conduction during operation without a signal being applied to a base connection of this transistor.